1. Field
The field of the invention is the harvesting of brine shrimp cysts from bodies of highly salt concentrated water, such as found in the Great Salt Lake.
2. State of the Art
Brine shrimp eggs are contained within protective spherical cysts which, in the species of concern, float in dense concentrated brine. The cysts exist in huge numbers and have in fact been harvested from shoreline deposits. However, this method of harvest typically results in the inclusion of much debris and foreign material, including sand and the like. This material must subsequently be removed by washing and other procedures at considerable expense before the cysts are in condition for shipment. Shrimp eggs are ultimately caused to hatch and develop into the shrimp, which are then utilized as food for use in shrimp farms and the like producing food for human consumption. More recently, a great deal of interest has developed in harvesting the shrimp cysts distantly from shore to avoid the contamination from foreign material. The cysts inhabit the top fraction of an inch of the surface of the salt water. They may be harvested as by manual net dipping, utilizing 120 mesh material and the like. Such harvesting methods are practical, but are undesirably labor intensive. Accordingly, other devices have been conceived based upon pumping the cyst rich top layer of water into porous cloth bags or the like, with the brine subsequently draining away and leaving the cysts within the bags. However, the direct pumping of the surface layer appears to be impractical because the available pumping apparatus ingests far too much water along with the cysts, making the bag straining procedure unduly time consuming and inefficient. Accordingly, devices have been conceived and used which attempt to efficiently concentrate the cysts within the brine before pumping into the final receptacle bags. One such device is disclosed in U.S. Pat. No. 4,839,062, being a raft-supported cyst collection device in a funnel configuration. The funnel is submerged in the water so that a portion of its leading upper edge is below the cyst-containing layer of water. The device then depends upon forward motion of the raft to ingest the cyst-containing layer of water, hopefully concentrated sufficiently to be a slurry. The funnel outlet is connected to a hose and pump system to move the slurry from the funnel into the final cyst collection bags. The success or efficiency of the system depends upon maintenance of the funnel level, which is done by a crank and screw device which adjusts the entire funnel in elevation. This adjustment must be constantly changed because of swells, either occurring from wind or from the forward motion of the raft. A somewhat improved device is found in U.S. Pat. No. 4,998,369, which includes a similarly shaped funnel collection device which has however a forward movable edge which can be adjusted in elevation to allow the shrimp laden layer to flow inwardly to the pit of the funnel. No forward motion is needed with this device to make initial collection of the floating cysts. This patent also discloses various onboard means associated with the cyst collection pontoon boat, to concentrate the cyst containing salt water to some extent. These devices include a pressurized system wherein pressure is used to force greater amounts of the salt water from the cysts at an intermediate point in their pumped transfer from the sump to the eventual cyst collection bags. However, further shore based cleaning and dewatering of the salt water is required, using fresh water, before final drying of the cysts into the form suitable for containerizing. In U.S. Pat. No. 5,042,187, a floating boom is placed to form an enclosure around a floating shrimp egg colony to be harvested. An associated pontoon boat is fitted with manually cranked roller arrangements to reel the boom toward the boat, shrinking the enclosure and concentrating the shrimp cysts within the upper inches of water. Instead of a sump and an associated slurry pump, as used in previously discussed patented devices, the concentrated slurry is dipped from the water by conveyor mounted screens of porous material, to dewater the collected cyst slurry to some degree before depositing it into water porous collection bags. The conveyor mounted sieves retain substantially all foreign matter, which must be removed in a later operation. With this procedure, the boom is used to encircle individual floating colonies of brine shrimp; the harvester boat must frequently move from one such colony to another to amass a significant harvest. Typically, the individual colonies of cysts are wind blown and scattered about the surface of the water.
Clearly, a need continues to exist for improved apparatus and methods for offshore harvesting of brine shrimp cysts which does not require constant movement of the harvester vessel about the body of water, but permits the harvest of widely dispersed floating cyst colonies from the vessel anchored in a single location.